Safety circuit cut-out



Patented June 16, 1925.

' UNITED STATES PATENT 7 OFFICE.

MARTIN H6CHST1DTER, OF S GRAVENHAGE, NETHERLANDS, ASSIGNOR TO N. V. LIJN PROTECT-IE, OF S GRAVENHAGE, NETHERLANDS, A CORPORATION OF THE NETHER- LANDS.

SAFETY CIRCUIT CUT-OUT.

Application filed August 24,1921. Serial No. 494,833.

(GRANTED UNDER THY PROVISIONS OF THE ACT OF MARCH 3. 1821, 41 STAT. L, 1313.)

To all whom it may concern:

Be it known that I, MARTIN Hoons'rls'n- TER, a citizen of the German Empire, residing at s Gravenhage, Netherlands, have invented certain new and useful Improvements in Safety Circuit Cut-Outs (for which I have filed applications in Netherlands May 17th, 1920, Ser. No. 14,830; Germany, filed May 22nd, 1920, Ser. No. 81,083), of which the following is a. specification.

Safety apparatus for the automatic disconnection of faulty sections of electric supply circuits are known wherein auxiliary lines are arranged parallel to the main lines and connected at the ends of the sections through transformers to the main lines. The transformers are so dimensioned and connected relatively together as to generate a shifting of potential, whilst leaving the auxiliary line still carrying the current of the supply circuit.

In the normal working of the supply circuit, the transformers produce astate of equilibrium in the two lines so that therefore the ratio between the currents in the main line and the auxiliary line is constant for all loads.

If this ratio is varied by the occurrence of a fault, differential relays that are included in the line circuit-s, come into operation and cut out the faulty section.

In the aforesaid known apparatus it is essential that the two transformers of one section shall be different from each other. The manner in which this difference is to be selected in order to produce the most favourable conditions, is the object of the present invention.

This present invention provides an improved means for keeping constant the ratio between the effective values of the currents in the two conductors from a low working current up to the greatest overload. This improved means consists in making transforming ratio of at least one of the two coupling transformers of the line section smaller than the impedance ratio between the main line and the auxiliary line.

Some practical embodiments of this in vention are illustrated in the accompanying drawings, in which- Fig. 1 illustrates the connection of the transformers of the safety apparatus;

Fig. 2 illustrates a scheme of connections of the improved apparatus wherein the primary windings of both transformers carry the undivided current;

Fig. 3 illustrates another modification in which the primary of one transformer carries the divided current whereas the primary winding of the other transformer carries the undivided current;

Fig. 4 illustrates a. line section arranged similar to that shown in Fig. 1, but having two transformers of different size core; and

Fig. 5 illustrates an arrangement also similar to Fig. 1. but having resistances arranged in parallel to the transformer windings. I

In Fig. 1 the current flows from the switch 11 to the branching-off point 17 and thence in one direction through the primary winding 13 line section 1, primary winding 23 and the branching-off point 27 to the switch 22; and in another direction from the branching-off point 17 through the secondary winding 14, branch line 2, secondary winding 24 to the branching-off point 27 and thence to the switch 22. The secondary windings 14f. and 24 are connected in the opposite way. In this connection therefore both primary windings carry only one branch current.

Switches 11 and 22 are operated by differential relays which receive their current from transformers at their respective end of the section. For this purpose for instance the right hand end of the section is provided with three differential relay coils 33, two of which are located in the main or auxiliary line respectively, the third being inductively connected with the first two and in circuit with tripping coil 35. This coil may operate cut-out switch 11 in any conventional manner known in the art.

The other end of the line section is correspondingly provided with differential coils 32 and tripping coil The cut-out switches 11 and 22 shown in the remaining figures to be described presently, maybe similarly actuated, as shown.

In order to assure that the transformers shall give a determined voltage, for instance two hundred volts, even when there is only a very small working current flowing in the line sections, and to assure that this voltage,

in the case of full load and ever so great overload, shall not appreciably lncrease or at least shall not exceed a deternnned value,

the transformers are constructed in such a manner that; their iron C1110}; shall hecoine magnetically saiura d even with a very low working current (:5 to it) per cent). t is advisable to give to hoth traus'l ormers a smaller transforming ratio than the i111 11th ance ratio betwetn the main line and t1 auxiliar line but it is nece try that ll 1?; he the case at least tor one ot the twotrans torine B traustorniing atio of the transformers 1 meat to im ill the ratio ot the number of turns located in the auxiliary line to the number of turns of cated in the main line. The 'loll serve as an. era up e of how i transformer arrangement ilhr ure 1 may he executed in pr: as the transforming ratio anti 1 ratio above rel'erred to is concern Assuming that the cro sectional area oil the main line he 30 times :hat. (it the an):- iliary line area, then the dance ratio between the auXiliar line an 1e main line has the value 30. Then in a transformer arrangement such as is shown in Figure l the following ratios oi the transformers 11111:; be chosen.

Rig/1t hand or first its coil lo- Primary winding (13) 1-12; turns Secondarl winding (ll) "81 turns Left hand or "sew/115" z' mn-sfomzew.

Primary winding 6 turns Secondary winding 21*) t 9 turns Thus the ratio of the first "rtnstoriner is which value is indeed smaller than l5 or o hetwe 11 the more, the

one-half of the impedance rati auxiliar and main line. Fur

number 01? turns, (5, or the ing 2;) of the second t ansh 1 than the number of turns, 12, of the nrarv winding l?) of the first transliornier. On the other hand, the number of turi tit 1 c V t'anst'oriner is greater than the number of turns. St. of the secondary w nding; it of ther, the two currents remain almost co1nplete y in phase with each other. The equi- .lihrinni between the currents in the main inn and the auxiliary line is extraordinarily stable and the dillerential relays an he The last ra ted. in

given a high degree of sensitivcness. co tions oi the apparatus il .1 15. l. are re idercd 11articnlarl :l'avom'ahle as l'tji'ill'tS the e111 lihrium hetween the two li'ies and t 1e absence of shifting ol phase 1 iarv line relat ivclv to the current 1 i L "1 the anxil 1 1c main line, h making thetransl'orming 1: o (11' too lirst t'rans'tormer ol' one line section innaller tln 1,1 the ha ol' the impedance r: "io oi the two lines, and l'urther ov giving to the section t'rans'tornter, whose secomlarv winding is connected in the reverse way to the Sicfilitlttlb' winding ol the, first trans former, a smaller nnmher of primary winding tur and a arger number ol secondary windin turns than to the l'irst trans'lormer. lily the distinctive designation lirst transtermer and V "'l" translormer, used hereinafter and in the annexed claims, 1 mean to imply a distinction between the two transformers,

inso raras in th actual connection of the two transformers in one line section, the iron core of the first transformer is mag: netimd by its two coils in different; senses, whereas the iron core of the second trans former is magnetized h these two coils in the same sense. These designations thus refer solely to the actual additions of magnetization in the transformers themselves, and are independent of the direction ot the transmission of energy in the line section, that is to 3' it is immaterial at which end of the line section the lit-st or second transformer is situated.

l v this improved arrangement, the same 11 agnetic conditions are produced in the tirst and second tra .rmers of a line section atall loads. The improved apparatus ensures an exact equalization, and has ver v grrat practical advtnag for instance the releasdevices (rela 111:1 he adjusted with extraordinary isitiveness because in the normal working, not only the r: tio

1' an: spondinglv dinerent', or both means may he comhin gd together. Incidentally the saturation oi? the tran formers has also the ad vantage that acct lin to experience, such saturated tr: "ormei oll'er to the high trequencv waves and impact waves that traver=e the line, a smalln' resistance than nnsurated iron devices. An exact equalization of the two transformers of 11 line section relatively to each other and to the impedance ratio between the main line and the auxiliary line, may also be produced by the following constructional forms which offer constructional advantages.

The operation of the apparatus shown in Fig. 2 is the same. as that in Fig. 1, except that the winding ratios of the transformers must be calculated differently. Of course, the iron relations may also be varied; but in the following description for the sake of simplicity, it is assumed that the iron dimensions of both transformers are the same. If the iron cores 15 and 25 are equal, the two secondary windings 14 and 24 will have equal numbers of turns. The number of primary turns in the second transformer 23, 24, 25 must again, as above, be smaller than the number of primary turns in the first transformer 13, 14, 15. By reason of the fact however, that the secondary windings of the two transformers must not be made different from each other, but are given the same number of turns, an advantage is gained for the mass production of certain types of transformers.

Fig. 3 illustrates another modification wherein the primary winding 13 of the transformer 13, 14, 15 carries the divided current, whereas the primary winding 23 of transformer 23, 24, 25 carries the undivided current. The branching-off point 17 for the line 2 is situated, in the case of transformer 13, 14, 15 between the switch 11 and the primary winding 13, whereas the branching-0ft" point 26, in the case of the other transformer, is situated between the two primary windings. This arrangement no doubt loses the advantage of equal numhers of turns of secondary windings. They must be made different from one another in such a manner that the number of turns of the coil 24 of the second transformer is equal to the sum of the numbers of turns of coils 13 and 14. This modification is advantageous inasmuch as that with otherwise equal conditions, the number of turns of the coil 24 is rather smaller than in the case of modification shown in Fig. 1. It is also possible to employ for the transformers iron cores of different dimensions, or to allow of using a plurality of transformers at each end of the line section; each transformer being subdivided into a plurality of transformers or being provided with a plurality of iron cores as desired. In this case, however, at least two transformers of one line section must be different from each other, and they must be constructed with different iron cores,so long as by correct selection of the numbers of turns in proportion to the iron cores and in proportion to the impedance of the main line of the auxiliary line, care is taken that the magnetic induction in the iron cores is always the same. These conditions can be calculated in advance.

Fig. 4 illustrates an arrangement of this kind. The secondary coils 14 and 24 which are connected to the branching-off points 17 and 27 of the main line section 1, are again connected in opposite ways. As before, the problem consists in so constructing these transformers that the most uniform possible voltage shall be generatedat points of the line section between the parallel lines 1 and 2, and that, nevertheless, the normal distribution of a current between the main line and the auxiliary line shall be main tained for all loads on the line section. Further, all shifting of phase and distortion of the two coils in the lines 1 and 2 relatively to each other shall be avoided as far as possible. That is to say, in normal working the transformers must generate a difference of potential between the main line and the auxiliary line without exerting any appreciable influence upon the current flowing through the said lines. Assuming the case where it desired to protect a line carrying very large current; the main line and the auxiliary line will therefore be very unequal, so that the auxiliary line will carry only a comparatively weak branch current. In this case it is advisable to mount the transformers directly upon the conductor bars or upon a conducting tube. This is illustrated in Fig. 4 where the iron cores 15 and 25 consist of rings which are simply slipped on to the line portions 13 and 23, and carry the secondary windings 14 and 24. In order to produce the desired state of equilibrium between the main line and the auxiliary line with the use of only one primary winding for each, the iron rings of the transformers must have different diameters because the desired equilibrium cannot be attained solely by the choice of the turns in proportion to the impedance ratio between the lines or by varying the crosssections of the iron. The requisite length of the path of the lines of force in both iron cores can be calculated in advance in connection with the impedance ratio between the main line and the auxiliary line and the numbers of winding turns of the transformers, and the cross-sections of the iron.

The arrangement shown in Fig. 4 is particularly adapted for building up the transformers out of part transformers by slipping a plurality of iron rings on to the common conducting tube 13 or 23. The rings may be provided either singly or in common with the secondary windings. In this way transformers can be built up from a small number of existing patterns in a simple manner for the various lengths of line and current. The improved apparatus particularly advantageously permits of a great freedom of design of the transformers Lilland their electrical connections neycrtheless, owing to the equal magnetic induction, the ratio of the currents in the parallel lines, is maintained perfectly independent of the condition of load on the line section. Thus it is possible to adapt to a very full extent the construction of the tranformers to the existing electrical and space conditions. For practical working it may be advisable to bridge the trans'fin'mers of one or both sides with ohmic 11' capacity resistances. By lmilding-in the resistances care must be talten of course not to interfere with the equilibrimu of the. currents in the main line and auxiliary line, and not to diminish the sensitiveness of the apparatus as regards discom'iection in the use of a fault.

Fig. 5 illustrates the connections. The resistance 28 is connected in parallel with the primary winding 13 and resistance 29 is connected in parallel with the secondary winding 't-t-. The resistances 3t) and 31, are connected in parallel with the coils Q3 and i i of the other transformer. (oniparativeiy very small ohmic values can be employed for the primary and secondary resistances. Likewise the prin'iary ohmic values may be chosen fairly independently of the second ary ohmic yalucs. However the ratio of the two primary ohmic yalues to the two secornlary ohmic values must be the same as the ratio of the windings to which they are connected in parallel. Thus,, for example if the second transformer has one half the number of primary winding turns and twenty per cent more secondary windings than the first transformer, then this primary parallel resistance must be equal to one half the. ohmic value of that. of the primary resistance of the first transformer, and its secondary resistance must have an ohmic yalue twenty per cent higher than that of the secondary resistance of the first transformer.

That I claim is 1. In an automatic safety circuit cut-out system for line sections of the chhractcr described, having a main line and an auxiliary line in each line section and trans formers at the ends of each line section for coupling the auxiliary line to the main line, ant. adapted to cause the cut-out operation in case of line disturbance. the transformer ratio of at least one of said coupling transformers being smaller than theimpedance ra'io between the main and the auxiliary line.

2. In an automatic safety circuit cut-out em or line sections of the character described. having a main line and an auxil- '-try line in each line section and transormers at the ends of earn line section for co pling the auxiliary line to the main line. and adapted to cause the cut-out operation in case of line disturbance the transformer ratio of at least one of said coupling transformers being smaller than the impedance ratio between the main and the auxiliary line, said transforn'ieis being suitably dimensioned and connected to each other in case of line disturbance. the transforna-r ratio of at least one of said coupling transformers being smaller than the impedance ratio between the main and the auxiliary line. the first transformer of each line section having its primary and secondary windings arranged to produce opposing 'netic fields and having the transformaratio between its windings smaller than 'l'f of the impedance ratio between the main and the auxiliary line section.

in an automatic safety circuit cut-out system for line sectil'ins o'f'the. character dcscribethliaying a mainline and an auxiliary line in each line section and transformers at the ends of each line section for winding the auetiliary line to the mainline, and adapted to cause the cut-out operation in case of line disturbance. the transforn'ier ratio of at least one of said coupling transformers being smaller than the im icdance ratio between the main and the auxiliary line. the second transformer of each line section having a smaller number of primary windings than the firs-t" transformer, and a number of secondary windings larger than the number of secondary windings of the first transformer.

5. In an automatic safety circuit cut-out system for line sections of the character descrihed, having a main line and an auxiliary line in each line section and transformers at the ends of each line section for coupling the auxiliary line to the main line..and adapted to cause the cut-out operation incase of line disturbance. the transformer ratio of at least: one of said coupling transformers being smaller than the impedance ratio between the main and the auxiliary line. the second transformer of each line section having a smaller number of 1 )rimary windings than the first transformer. and, a number of secondary indings equal to the sum of the number of secondary and primary windings of the first transformer.

6. In an automatic safety circuit cut-out system for line sections of the character do scribed. haying a main line and an auxiliary line in eachv line section and transformers at the ends of each line section for coupling the auxiliary line to the main line, and

adapted to cause the cut-out operation in case of line disturbance, the transformer ratio of at least one of said coupling transformers being smaller than the impedance ratio between the main and the auxiliary line, at least one of said transformers being built up of a plurality of part transformers, at least two of each part transformers of a line section being different from each other.

7. In an automatic safety circuit cut-out system for line sections of the character described, having a main line and an auxiliary line in each line section and transformers at the ends of each line section for coupling the auxiliary line to the main line, and adapted to cause the cut-out operation in case of line disturbance, the transformer ratio of at least one of said coupling transformers being smaller than the impedance ratio between the main and the auxiliary line, and resistances disposed in shunt to the windings of said transformers, the ratio of the ohmic values of the two primary resistances to the secondary resistances being the same as the ratio of the windings to which they are shunted.

In testimony whereof I afiix my signature.

MARTIN HOGHSTADTER. 

